Wilms tumor is an embryonal kidney cancer of children that exhibits aberrant nephrogenesis and thus provides a model system to study the molecular events underlying the developing kidney. This tumor is associated with anomalies in the urogenitary system and present evidence suggests a shared genetic origin for Wilms tumor and associated urogenitary abnormalities. We have cloned and characterized two linked, divergently transcribed genes, WT1 and WIT-1, implicated in Wilms tumorigenesis by virtue of being deleted or mutated in tumor DNA. Germline mutations in a single WT1 allele can result in nephropathy, ambiguous genitalia and cryptorchidism (the Denys Drash syndrome). Loss of expression from both alleles results in Wilms tumor. In the normal developing kidney, WT1 and WIT-1 are expressed only in the condensing metanephric mesenchyme or developing glomeruli. Thus these genes must respond to induction following interaction of the metanephric mesenchyme and the epithelial ureteric bud and likely regulate the expression of other genes involved in differentiation and morphogenesis. Our long term objective is to determine how the WT1 and WIT-1 genes function in nephrogenesis and pathogenesis of the kidney and urogenitary system. In order to determine how the temporal and spatial expression of the WT1 and WIT-1 genes is controlled,to define downstream targets for regulation by these genes, and describe the functional consequences of aberrant the expression of these genes, we propose to establish and study animal and cell culture models of nephrogenesis. The specific aims are: 1) To define the cells of origin of expression of the WT1 and WIT-1 genes and their candidate target genes using in situ hybridization and immunocytochemistry thereby establishing expression patterns in the developing mouse embryo. 2) To delineate the promoter elements of the WT1 and WIT-1 genes necessary for the correct temporal and spatial expression we will map DNAse 1 hypersensitive sites and use this information to test different reporter constructs in transgenic mice. 3) To establish transgenic mouse lines in which the expression patterns of the WT1 and WIT-1 genes are perturbed by changing tissue specificity of expression or by maintaining spatial and temporal specificity but disturbing the relative levels of different forms of transcripts that are produced by alternative splicing. This integrated approach will allow us to elucidate fundamental molecular mechanisms of kidney development and provide insight into their dysregulation in kidney and urogenitary disease.